The treatment of the position of the teeth and the treatment of the position of the upper and lower jaw is generally possible by orthopedic and orthodontic means.
The orthopedic treatment or functional orthopedics has mainly been used in Europe. The appliances used in orthopedics are removable. They therefore produce forces on the teeth mainly intermittently and react as growth stimulators intermaxillary and intramaxillary. The exact positioning of teeth is, however, not possible because there are only point contacts between appliances and teeth.
The orthodontic treatment is characterized by its fixed appliances. The forces applied by fixed appliances react on the teeth in all three dimensions at the same time. The position of the upper jaw and its teeth in relation to the lower jaw and its teeth is handled by additional intermaxillar and extraoral appliances, like elastics and headgear or facebow. In stimulating growth and growth direction of jaws, muscles, habits and teeth, fixed appliances seem to be in different situations less effective than removable appliances, but are highly superior in the detailed positioning of teeth in their special function.
The vast majority of all cases represents a combination of growth problems, like position of the jaws, and wrong positioned teeth in the upper and lower jaw. Therefore a combined therapy with both appliances, using primarily removable appliances and in particular for dental anomalies with rest growth problems fixed appliances, is indicated.
Historically functional orthopedics in its narrow sense has been developed in Europe and comprises essentially removable appliances only, whereas orthodontics has been predominantly developed in the U.S.A. and comprises mainly fixed appliances.
Functional orthopedics with its removable appliances works mostly with inductive, so-called functional forces with functional reaction on bones, teeth, muscles, parodontium and growth centers, whereas the orthodontic treatment with its fixed appliances usually influences biological structures mechanically.
The fixed appliances consist mainly of two basic units. The one part, namely the bracket or band, is firmly fixed on each tooth and contains a slot with a specific cross-section. The other part, namely the archwire, is fixed into the slot and combines all teeth of a jaw. The bands originally consisted of metal rings onto which attachments with slots were welded. Brackets are essentially only these attachments without the band or ring, and are directly fixed on each tooth by adhesive materials.
By using a rectangular slot in the brackets, which are fixed on the teeth with a fixed rectangular wire in the rectangular slot, the effect of the force is acting three-dimensionally. The individual teeth can be influenced in their height, in their angulation, and in their axial inclination.
The brackets have to be placed extremely accurately in height and angulation to prevent unwanted extrusions or angulations of the different teeth when a straight wire is ligated. The third dimension providing a torque acting on a tooth is applied differently in the different techniques. The displacement of the axial inclination of a tooth can either be provided by a torsion in the wire or, if straight wires are used, by an adequate inclination of the slot in the bracket.
The different techniques in orthodontics differ mainly in different angalations and torques in the slots of the brackets. When using a straight wire without torsion, the final axial position of the tooth is essentially predetermined by the angular position of the slot in the bracket. The most famous techniques are the "Jaraback", "Rickets", "Alexander", "Hilgers", and "Roth", Technique. A survey of the different techniques is to be found for example in the handbook "Handbuch fur die kieferorthopadische Praxis, Band II, des Berufsverbandes Deutscher Kieferorthopaden 1988".
All these orthodontic techniques have in common both a rectangular slot and a rectangular archwire. With the exception of the Roth technique, a slot of 0.018.times.0.022 inches is used, and rectangular wires having a size of 0,016.times.0.016, 0,016.times.0.022, 0,017.times.0.022 and 0.018.times.0.022 inches. In the Roth technique, a slot with a size of 0,022.times.0.025 inches and archwires up to this size are used. Note that all commercial archwire cross-sections are given in inch or 1/1000 inch; 1 inch=25.4 mm.
To reduce the enormous forces from one tooth to the other, there were used so-called multiloop arches particularly in the initial levelling phase of the Jaraback technique. In putting more wire, namely a loop, inbetween the distance from one tooth to another the amount of force can be reduced. The disadvantages of this multiloop technique are the following: It is extremely difficult to bend a wire, to activate the wire, and to control the forces on the teeth and their movement, and it takes a great deal of time to obtain its shape, which a patient often will not accept. Additionally these loops may injure the soft tissue directly, and tooth brushing is hardly possible with the consequence of following damage to the teeth by various decalcifications and inflammations of the soft tissues of the parodontium.
In order to avoid all these disadvantages different and more elastic wires made of new alloys were developed in order to allow the handling of the teeth with straight wires which are not broken by a loop. The problem to avoid the high forces has been tried to be solved by higher elasticity and lower stiffness of the alloys.
However, the main problem in handling these wires is, surprisingly, their elasticity, because it is more or less impossible to bend any individual demand into these wires. i.e. to bend the known wires in such a way that the individual requirements are fulfilled. Therefore they are useful only for a very short treatment period or for some abnormal situations.
In addition the span, the distance from tooth to tooth, has a very small biological variability. This means that even if the elasticity of a wire may be extremely high, every elastic wire with a cross-section of 0.016.times.0.022, 0.017.times.0.022, 0.018.times.0.022 or even 0.016.times.0.016 inches, which are the common wire sizes, in a slot of 0.018.times.0.022 inches separated by a span of approximately 4 to 6 mm (0.16 to 0.24 inches) will still cause enormous forces. These forces which are directly influenced by the physical requirements of the size of the wire and the span are not sufficiently controllable or adjustable and are not within biological limits.
In numerous articles damage and problems with too high forces are described. They range from root resorptions, damage to the parodontium, necrosis by lack of blood supply and resulting loss of tooth movements (ankylosis), up to the failure of handling a case because too high a force moment very often does not cause the required intrusion in the front but rather an extrusion of the molars by bigger rotation moments or torques for example. A mismanagement in this way may cause temporomandibular joint problems and muscle diseases with headache. The generally accepted biological demands in this field are e.g. described in the articles of Kaare Reitan, D.D.S., U.S.D., Ph.D., e.g. in the treatise "Biomechanische Prinzipien der Gewebsreaktion" in "Grundlagen und moderne Techniken der Kieferorthopadie", pages 149 to 279, and by other scientists.
A summary of these ideas is to be found in the book "Current Principles and Techniques" by T. M. Graber/B. F. Swain.
The required forces should work simultaneously in three dimensions, be controllable as to the wanted direction and amount of movement and cause less damage to biological tissue. This cannot be achieved in the common systems, even not by means of the more elastic wire alloys discussed above. While round wires with smaller diameters, which consequently cause weaker forces, are available, these round wires do not work three-dimensionally and are thus useful only for the initial levelling period.